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271.
Over the past decades, a number of water sciences and management programs have been developed to better understand and manage the water cycles at multiple temporal and spatial scales for various purposes, such as ecohydrology,global hydrology, sociohydrology, supply management, demand management, and integrated water resources management(IWRM). At the same time, rapid advancements have also been taking place in tracing, mapping, remote sensing, machine learning, and modelling technologies in hydrological research. Despite those programs and advancements, a water crisis is intensifying globally. The missing link is effective interactions between the hydrological research and water resource management to support implementation of the UN Sustainable Development Goals(SDGs) at multiple spatial scales. Since the watershed is the natural unit for water resources management, watershed science offers the potential to bridge this missing link.This study first reviews the advances in hydrological research and water resources management, and then discusses issues and challenges facing the global water community. Subsequently, it describes the core components of watershed science:(1)hydrological analysis;(2) water-operation policies;(3) governance;(4) management and feedback. The framework takes into account water availability, water uses, and water quality; explicitly focuses on the storage, fluxes, and quality of the hydrological cycle; defines appropriate local water resource thresholds through incorporating the planetary boundary framework; and identifies specific actionable measures for water resources management. It provides a complementary approach to the existing water management programs in addressing the current global water crisis and achieving the UN SDGs. 相似文献
272.
Six holes were drilled to depths of 30–69 m in the shallow lagoon of Aitutaki in the southern Cook Islands. One hole encountered pervasively dolomitized reef limestones at 36 m subbottom depth, which extended to the base of the drilled section at 69·3 m. This hole was drilled near the inner edge of the present barrier reef flat on the flank of a seismically defined subsurface ridge. Both the morphology and biofacies indicate that this ridge may represent an outer reef crest. Mineralogy, porosity and cementation change in concert downhole through three zones. Zone 1, 0–9 m, is composed of primary skeletal aragonite and calcite with minor void-filling aragonite and magnesian calcite cement of marine phreatic origin. Zone 2, 9–36 m, is composed of replacement calcite and calcite cement infilling intergranular, intragranular, mouldic and vuggy porosity. Stable isotopes (mean δ18O=—5·4‰ PDB for carbonate; δD =—50‰ SMOW for fluid inclusions) support the petrographic evidence indicating that sparry calcite cements formed in predominantly freshwater. Carbon isotope values of —4·0 to —11·0‰ for calcite indicate that organic matter and seawater were the sources of carbon. Zone 3, 36–69·3 m, is composed of replacement dolostone, consisting of protodolomite with, on average, 7 mol% excess CaCO3 and broad and weak ordering X-ray reflections at 2·41 and 2·54 A. The fine-scale replacement of skeletal grains and freshwater void-filling cements by dolomite did not significantly reduce porosity. Stable isotopes (mean δ18O=+2·6‰0 PDB for dolomite; maximum δD =—27‰ SMOW for fluid inclusions) and chemical composition indicate that the dolomite probably formed from seawater, although formation in the lower part of a mixed freshwater-seawater zone, with up to 40% freshwater contribution, cannot be completely ruled out. The carbon (δ13C=2·7‰) and magnesium were derived from seawater. Low-temperature hydrothermal iron hydroxides and associated transition metals occur in void space in several narrow stratigraphic intervals in the limestone section that was replaced by dolomite. The entire section of dolomite is also enriched in these transition metals. The metals dispersed throughout the dolostone section were introduced at the time of dolomitization by a different and later episode of hydrothermal circulation than the one(s) that produced the localized deposits near the base of the section. The primary reef framework is considered to have been deposited during several highstands of sea level. Following partial to local recrystallization of the limestone, a single episode of dolomitization occurred. Both tidal and thermal pumping drove large quantities of seawater through the porous rocks and perhaps maintained a wide mixing zone. However, the isotopic, geochemical and petrographic data do not clearly indicate the extent of seawater mixing. 相似文献
273.
Petrogenesis of Mafic to Felsic Plutonic Rock Associations: the Calc-alkaline Querigut Complex, French Pyrenees 总被引:1,自引:0,他引:1
ROBERTS MALCOLM P.; PIN CHRISTIAN; CLEMENS JOHN D.; PAQUETTE JEAN-LOUIS 《Journal of Petrology》2000,41(6):809-844
The Quérigut maficfelsic rock association comprisestwo main magma series. The first is felsic comprising a granodioritetonalite,a monzogranite and a biotite granite. The second is intermediateto ultramafic, forming small diorite and gabbro intrusions associatedwith hornblendites and olivine hornblendites. A UPb zirconage of 307 ± 2 Ma was obtained from the granodioritetonalites.Contact metamorphic minerals in the thermal aureole providea maximum emplacement pressure of between 260 and 270 MPa. Petrographiccharacteristics of the mafic and ultramafic rocks suggest crystallizationat <300 MPa, demonstrating that mantle-derived magmas ascendedto shallow levels in the Pyrenean crust during Variscan times.The ultramafic rocks are the most isotopically primitive components,with textural and geochemical features of cumulates from hydrousbasaltic magmas. None of the mafic to ultramafic rocks havedepleted mantle isotope signatures, indicating crustal contaminationor derivation from enriched mantle. Origins for the dioritesinclude accumulation from granodioritetonalite magma,derivatives from mafic magmas, or hybrids. The granitic rockswere formed from broadly Proterozoic meta-igneous crustal protoliths.The isotopic signatures, mineralogy and geochemistry of thegranodioritetonalites and monzogranites suggest crystallizationfrom different magmas with similar time-integrated Rb/Sr andSm/Nd isotope ratios, or that the granodioritetonalitesare cumulates from a granodioritic to monzogranitic parent.The biotite granite differs from the other felsic rocks, representinga separate magma batch. Ages for Quérigut and other Pyreneangranitoids show that post-collisional wrenching in this partof the Variscides was under way by 310 Ma. KEY WORDS: Variscan orogeny; Pyrenees; Quérigut complex; epizonal magmatism; post-thickening; maficfelsic association 相似文献